1. Field of the Invention
The present invention relates to methods of reducing the water production of a hydrocarbon well drilled through subterranean formations. More particularly it relates to such methods for selectively reducing the flow of subterranean aqueous fluids into a well while maintaining its hydrocarbon production.
2. Background
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
During the life cycle of a hydrocarbon (oil and gas) producing well, water is often produced along with the hydrocarbons. The amount of water produced from a well tends to increase over time with a concomitant reduction of hydrocarbon production.
Frequently, the production of water becomes so profuse that remedial measures have to be taken to decrease the water/hydrocarbon production ratio. The consequence of uncontrolled water production may be well abandonment.
Before hydrocarbons can be produced from subterranean formations, a production zone needs to be completed so that the well communicates with the hydrocarbon-bearing zone(s). Ideally, the hydrocarbon production zone does not communicate with the water-bearing portion(s). However, some hydrocarbon production zones may inadvertently communicate with a water-bearing zone. For example, water breakthrough may occur when a fracture goes out of zone and fractures into a water zone. Even if there is no actual initial fluid communication between the hydrocarbon production zone and the water-bearing zones of the formation, such communication may develop during the production of hydrocarbon. For example, water may be drawn upwardly from the water-bearing portion in a process known as water coning.
The production of water in hydrocarbon wells is an expensive problem. This is particularly difficult to deal with in open hole, horizontal wells, where there is no easy way to isolate and stop the water production, while allowing other parts of the well to produce hydrocarbons. The problem is especially vexing when water breaks through at the heel of the well and interferes with production of oil from places farther down in the wellbore.
Another complication from water inflow in wells relates to uncertainty of what zones or regions of the wellbore are producing water. Techniques are desired for detecting the water-producing zones so appropriate action can be taken.
Sometimes, the production of water cannot be isolated or stopped without expensive intervention to squeeze cement into perforations or to squeeze conformance gels into the matrix. This requires setting packers and/or placement with coiled tubing. These procedures are time consuming and expensive.
To remedy water-influx and/or coning, U.S. Pat. No. 3,719,228 discloses a method of treating a subterranean formation containing hydrocarbons and brine to stimulate the production of hydrocarbons. In accordance with this method, a pre-flush composition comprising an aqueous solution of rosin soap and fatty acid soap is injected into the formation. The pre-flush reacts with connate brine to produce a precipitate that blocks the brine-bearing passages. The pre-flush composition does not react with hydrocarbons, thereby allowing hydrocarbon-bearing passages to remain open.
Another method is disclosed in U.S. Pat. No. 4,617,132. In accordance with this method, a sandstone formation is first contacted with an aqueous solution containing a water-soluble anionic polymer having a molecular weight greater than 100,000. Then, the anionic polymer is contacted with a fluid containing a water-soluble cationic polymer having a molecular weight greater than 1,000. As a result of the contact of the anionic with the cationic polymer, coacervation occurs between the two polymers which reduces the amount of the anionic polymer removed from the formation by fluids produced there from. The presence of stabilized polymer in the formation reduces the water/oil ratio by reducing the permeability of the formation to water in the wellbore area.
U.S. Pat. No. 5,146,986 discloses another method of selectively reducing the permeability of a subterranean formation. The formation is contacted with a hydrocarbon carrier liquid containing a surface active agent. The surface active agent is believed to adsorb on the walls of the interstitial passages in the formation, as a result of which, the flow of water through the passages is reduced.
U.S. Pat. No. 5,150,754 discloses a method of selectively injecting into a hydrocarbon-bearing zone a petroleum mixture capable of forming a solid gel that degrades over a designated period of time. Then, an aqueous gel-forming mixture is injected into a water influx zone of the formation. Upon degradation of the first gel, production of hydrocarbons can continue.
Another method, disclosed in U.S. Pat. No. 5,203,834, comprises the steps of injecting into a well a gas, a polymer composition capable of forming a foamed gel with the gas, and a delayed gel degrading agent capable of opening pathways in the gel.
Furthermore, K. E. Thomson and H. S. Fogler published in SPE Production and Facilities, May 1995, pp. 130-137, a proposed method that uses an injection backflow and shut-in procedure, as well as a slow-reacting silica based diverting agent. The backflow step is described as a miscible displacement of the agent before the onset or completion of the gelation.
U.S. Pat. No. 6,803,348 issued to Jones et al. and U.S. Pat. No. 6,920,928 issued to Davies et al. disclose hydrophobically modified polymers for water control and methods of using these polymers in water control. These patents are assigned to the present assignee and are incorporated by reference in their entirety. The polymers disclosed in these patents are based on polymers having side chains that can be cross-linked with chromium(III), zirconium(IV), or organic cross linkers (e.g., hexanal) in aqueous environments, but not in hydrocarbon environments.
While these prior art methods have been successfully used to control water production, there remains a need for simpler and more convenient methods for controlling water production in a well.